1. Field of the Invention
The present invention generally relates to field emission display (FED) devices and, more particularly, to a new monolithic FED device and method of fabricating it.
2. Description of the Prior Art
Flat panel displays are of great interest for applications in laptop and palmtop computers, avionic and automobile consoles, information displays, high definition television (HDTV), to name but a few applications. Currently, much activity is focused on liquid crystal active matrix displays (LCDs) for use in many of these applications. LCDs have many shortcomings. They have low efficiencies, a restricted viewing angle, slow response time, and back lighting makes them thicker and heavier than desired for many applications. Field emission displays (FEDs) can solve all of these problems by bringing cathode ray tube (CRT) advantages into a flat panel configuration while eliminating the traditional CRT magnetic field and X-ray emission health concerns.
FEDs are a particular class of vacuum microelectronic devices (VMDs) and share the basic structure of those devices including a field emission cathode tip within an extraction electrode structure and an anode within a vacuum space. FEDs add to this basic structure a phosphor surface opposite the cathode tip and may include additional electrodes to control the electron current. A characteristic of FEDs common to VMDs in general is the requirement for precise alignment of the microstructure. This, in turn, has meant in the past complex and expensive manufacturing, making the FEDs uncompetitive with LCDs or the older CRT technologies. Several attempts have been made to develop a simpler and less costly technique for manufacturing VMDs and FEDs in particular. One example is described by C. A. Spindt in "A Thin-Film Field-Emission Cathode", J. Appl. Phys., vol. 39, no. 7, pp. 3504-3505 (1968), described in more detail hereinafter. Another approach is described in U.S. Pat. No. 3,665,241 to Spindt et al. uses orientation-dependent etching of single crystal materials such as silicon. Single crystal materials are, however, both expensive and limited in size. Fukase et al. in U.S. Pat. No. 3,998,678 describe another approach which uses isotropic etches to form the structures. In the Fukase et al. method, an emitter material is masked using islands of a lithographically formed and etch resistant material. The emitter material is then etched resulting in an etch profile which converges under the center of the mask in the form of a sharp tip. Smith et al. in U.S. Pat. No. 3,970,887 describe an oxidation process to form VMDs, and Gray et al. in U.S. Pat. No. 4,307,507 describe a process wherein a pit which is the inverse of the desired shape is etched in an expendable material and then used as a mold for the emitter material.
All of the techniques known in the art have limitations which, when applied to the manufacture of FEDs in particular, do not permit the manufacture of such devices with sufficient economies or precision to be competitive with current display technologies.